1. Field of Invention
This invention relates in general to production of oil and gas wells, and in particular to a system and method for subsea communication using radio frequency signals.
2. Description of Prior Art
Systems for producing oil and gas from subsea wellbores typically include a subsea wellhead assembly that includes a wellhead housing attached at a wellbore opening, where the wellbore extends through one or more hydrocarbon producing formations. Casing and tubing hangers are landed within the housing for supporting casing and production tubing inserted into the wellbore. The casing lines the wellbore, thereby isolating the wellbore from the surrounding formation. Tubing typically lies concentric within the casing and provides a conduit for producing the hydrocarbons entrained within the formation. Wellhead assemblies also typically include a production tree connecting to the upper end of the wellhead housing. The production tree controls and distributes the fluids produced from the wellbore.
Valve assemblies are typically provided within wellhead production trees for controlling the flow of oil or gas from a wellhead and/or for controlling circulating fluid flow in and out of a wellhead. Gate valves and other sliding stem-type valves have a valve member or disc and operate by selectively moving the stem to insert/remove the valve member into/from the flow of fluid to stop/allow the flow when desired. A subsea control module (SCM) can be provided with the subsea production system for operating the valves on the tree as well as other valves in the downhole production tubing and subsea manifold. Control commands directing SCM action may be initiated above the sea surface and transmitted down a communications link consisting of an umbilical that connects to an umbilical termination and leads connecting the umbilical termination to the SCM. The leads are susceptible to damage, either from the subsea environment or structurally from production or workover operations. Additionally, the leads can hinder wellhead assembly maintenance or repair, especially when a remotely operated vehicle is deployed subsea.
Currently control rooms for subsea wells can be located many miles away from the actual well and its associated production tree. Typically a production umbilical links the production tree with the control room. During workover operations a workover umbilical is lowered from a floating rig or work boat and leads from the workover umbilical are connected to the tree after disconnecting the production umbilical. Alternatively, without disconnecting the production umbilical, to actively control the production tree from the floating rig requires contacting the control room, usually by radio, to request production control relinquish priority to the workover crew. Communications issues sometimes interfere with passing control authority to the workover, that can harm production or be hazardous to personnel or equipment.